package QizhongKaoshi;

import java.util.Scanner;
public class Kaoshi3 {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int n;
        n=scanner.nextInt();;
        double sum=0;
        for(int i=1;i<n+1;i++){
            sum+=1.0/(i*2);
        }
        System.out.println(String.format("%.4f",sum));
    }
}
